Computer data storage, in particular random access memory (RAM) has become an increasingly important component of electronic hardware. There are various distinct types of memory devices, distinguished by their speed and data retention characteristic. Dynamic random access memory (DRAM) is a volatile memory characterized by a destructive read. This means that it is necessary to supply voltage to the memory bits at all times, or the information will disappear. Furthermore, each memory element has associated with it a transistor. Static random access memory (SRAM) stores data in a bistable flip-flop, commonly consisting of cross-coupled inverters. It is called “static” because it will retain a value as long as power is supplied. It is still volatile, i.e. it will lose its contents when the power is switched off, in contrast to ROM. SRAM is usually faster than DRAM, but each bit requires several transistors (about six), so that a lesser number of bits of SRAM fit in the same area as compared to DRAM.
Erasable programmable read only memory (EPROM) is a type of storage device in which the data is determined by electrical charge stored in an isolated (“floating”) MOS transistor gate. The isolation is good enough to retain the charge almost indefinitely (more than ten years) without an external power supply. The EPROM is programmed by “injecting” charge into the floating gate, using a technique based on the tunnel effect. This requires higher voltage than in normal operation. The floating gate can be discharged through UV-illumination or electrically (EEPROM). Usually bytes or words can be erased and reprogrammed individually during system operation. EEPROM is more expensive and less dense than RAM. It is appropriate for storing small amounts of data which is changed infrequently.
Most of these devices require complex silicon processing steps and a dedicated device architecture for the various memory types. It would therefore be desirable to provide a material with a predictable memory effect adaptable for short-term and long-term data retention and suitable for producing reliable and inexpensive memory and/or switching devices for data storage and data manipulation.